The major objectives of power control are to guarantee a required received signal to noise ration (SNR) by compensating path-loss and fading of channel and to provide a high system throughput with proper link adaptation. In addition, inter-cell interference can be also handled by power control. In the 3rd generation partnership project (3GPP) long term evolution (LTE) system, the uplink power control is based on open-loop power control with closed-loop correction. The open-loop power control is handled by a user equipment (UE) and the closed-loop correction is done by an evolved Node B (eNB). FIG. 1 shows basic concept of uplink power control in LTE system.
As shown in FIG. 1, the uplink power is mainly measured by UE in open-loop manner and the eNB can adjust the uplink power by closed-loop correction factor Δ.
The exact formula can be expressed as the following Math Figure 1.PPUSCH(i)=min{PMAX, 10 log10(M(i))+Po(j)+α(i)·PL+ΔTF(i)+f(i)} [dBm]  [Math Figure 1]
In Math Figure 1, at a time index i, the PMAX denotes the maximum allowed power, and it depends on the UE class. In addition, M(i) is decided according to allocated resource blocks which can varied from 1 to 110 and it is updated in every subframe. The α·PL is used as path loss compensation term where PL denotes downlink path-loss estimated by UE and is scaling value. The αis equal to and less than 1 and is expressed as 3 bit value. If α=1 is satisfied, path loss is fully compensated and If α<1 is satisfied, path loss is fractionally compensated.
In addition PO(j) is calculated as the following Math Figure 2.PO=PO_CELL_SPECIFIC+PO_UE_SPECIFIC   [Math Figure 2]
In the Math FIG. 1, f(i) is UE-specific parameter controlled by the eNB. In addition, the power control for Physical Uplink Control Channel (PUCCH) can be defined as the following Math Figure 3.PPUCCH(i) =min{PMAX, P0_PUCCH+PL+h(nCQI,nHARQ)+ΔF_PUCCH(F)+g(i)} [dBm]  [Math Figure 3]
The parameter ΔF_PUCCH(F) is provided by higher layers. Each ΔF_PUCCH(F) value corresponds to a PUCCH format (F) relative to PUCCH format 1a. In addition, h(n) is a PUCCH format dependent value, where nCQI corresponds to the number information bits for channel quality information (CQI) and nHARQ is the number of hybrid automatic repeat request (HARQ) bits.
For PUCCH format 1,1a and 1b, the following Math Figure 4 is satisfied.h(nCQI,nHARQ)=0   [Math Figure 4]
For PUCCH format 2, 2a, 2b and normal cyclic prefix, the following Math Figure 5 is satisfied.
                              h          ⁡                      (                                          n                CQI                            ,                              n                HARQ                                      )                          =                  {                                                                      10                  ⁢                                                                          ⁢                                                            log                      10                                        ⁡                                          (                                                                        n                          CQI                                                4                                            )                                                                                                                                        if                    ⁢                                                                                  ⁢                                          n                      CQI                                                        ≥                  4                                                                                    0                                            otherwise                                                                        [                  Math          ⁢                                          ⁢          Figure          ⁢                                          ⁢          5                ]            
In addition, for PUCCH format 2 and extended cyclic prefix, the following Math Figure 6 is satisfied.
                              h          ⁡                      (                                          n                CQI                            ,                              n                HARQ                                      )                          =                  {                                                                      10                  ⁢                                                                          ⁢                                                            log                      10                                        ⁡                                          (                                                                                                    n                            CQI                                                    +                                                      n                            HARQ                                                                          4                                            )                                                                                                                                                              if                      ⁢                                                                                          ⁢                                              n                        CQI                                                              +                                          n                      HARQ                                                        ≥                  4                                                                                    0                                            otherwise                                                                        [                  Math          ⁢                                          ⁢          Figure          ⁢                                          ⁢          6                ]            PO_PUCCH is a parameter composed of the sum of a cell specific parameter PO_NOMINAL_PUCCH provided by higher layers and a UE specific component PO_UE_PUCCH provided by higher layers.
δPUCCH is a UE specific correction value, also referred to as a Transmission Power Control (TPC) command, included in a PDCCH with DCI format 1A/1B/1D/1/2A/2 or sent jointly coded with other UE specific PUCCH correction values on a PDCCH with DCI format 3/3A whose CRC parity bits are scrambled with TPC-PUCCH-RNTI.
In addition to PUCCH and PUSCH, Sounding Reference Signal (SRS) is also power controlled as the following Math Figure 7.PSRS(i)=min {PMAX, PSRS_OFFSET+10 log10(MSRS)+PO_PUSCH(j)+α·PL+f(i)} [dBm]  [Math Figure 7]
In the Math Figure 7, PSRS is UE transmission power for SRS transmitted on subframe i.
For KS=1.25, PSRS_OFFSET is a 4-bit UE specific parameter semi-statically configured by higher layers with 1 dB step size in the range [−3, 12] dB.
In addition, for KS=0, PSRS_OFFSET is a 4-bit UE specific parameter semi-statically configured by higher layers with 1.5 dB step size in the range [−10.5,12] dB. Here, the Ks is a parameter for turning on or turning off ΔTF(i), where ΔTF(i) is a parameter for controlling power of PUCCH.
MSRS is the bandwidth of the SRS transmission in subframe i expressed in number of resource blocks.
f(i) is the current power control adjustment state for the PUSCH.
PO_PUSCH(j) is a value composed of sum of cell-specific power control parameter and UE-specific power control parameter, which are configured by higher layers.
FIG. 2 illustrates general uplink transmitter structure in LTE system. AS shown in FIG. 2, only one antenna port transmission is allowed in uplink LTE system and in a time, single channel of PUCCH and PUSCH can be transmitted.